The AvengersCaptain AmericaFantastic FourThor
These stories are independent of current Marvel continuity meaning two things. First, readers who follow the stories will have to just accept these one-off stories for what they are; more importantly, new readers should not be discouraged. Everything you need to know to follow what's going on is contained in the twelve pages of each issue. Furthermore, the four issues do not connect with one another in any fashion, so you don't have to worry about getting an incomplete set and not knowing part of the story.
The covers, I'm told, are recycled from previously published issues but the interior stories are all new. Each issue concludes with a one-page Mini Marvels backup story by Chris Giarrusso. In these, the Marvel characters are depicted in a cute little kid aesthetic and have issues one would expect from children superheroes. For instance, Thor is picked on for his style of speaking. Fans of Psych might think of these as akin to "The Adventures of Lil' Shawn and Gus."
The stories themselves are pretty simple and all-ages appropriate. Let's face it. There really isn't a whole lot you can do in eleven pages. I personally thought the Captain America issue was the best, as it sees Cap dealing with a terrorist cell leader whose prosecution is stymied by lack of physical evidence. Other stories have the Avengers take in (and be betrayed by) the villainous Ultron, Thor and The Thing team-up against the vandalizing Wrecker and Mr. Fantastic & the Invisible Woman's anniversary night spoiled by a rampaging Hulk.